1. Field of the Invention
The present invention relates to a driver having a storage device, an electro-optical device using the driver, and an electronic apparatus.
2. Description of Related Art
Usually, liquid crystal devices employ a method in which a storage device serving as a frame memory is provided in a display driver for driving a liquid crystal display panel and display data are read from the storage device and displayed. For example, at present, passive matrix liquid crystal display panels employ such gray scale display methods as the frame rate control (FRC) gray scale method, the voltage gray scale method, and the pulse width modulation (PWM) method. In the pulse width modulation method, one horizontal scanning period (1H) selected by a common driver for driving common electrodes (scanning electrodes) is divided into periods of a number that is equal to a prescribed number of gray scales and the period in which an on-waveform is applied is varied in accordance with the gray scale. The pulse width modulation method can control liquid crystal application voltages in such a manner that one horizontal scanning period (1H) is divided into periods of the number of bits constituting each unit of display data for gray scale display with weights given to the respective bits. On the other hand, there may occur a case that in applying voltages to the liquid crystal it is necessary to read out information of only a particular order bit such as MSB information or LSB information. At present, this type of driving method is used in the multi-line selection (MLS) driving method, for example, in which a plurality of common electrodes are selected simultaneously.
A description will be made of a case of driving, by the pulse width modulation method, a driver for processing four-gray scale (2-bit) display data. When information of the higher one bit of the two bits is necessary at a certain time point, information of the lower one bit which is unnecessary at that time point is also read out together with the information of the higher one bit.
As a result, useless power is consumed to read out the unnecessary information of the lower one bit; more specifically, it is consumed in a pre-charging operation for rendering the potentials of read lines in a constant, floating state and an operation of reading out memory cell information (current is consumed).